1. Field of the Invention
This invention relates to an electronic volume control apparatus which is remotely controlled by a remote controller. More particularly, to an electronic volume control apparatus which is remotely controlled based on a requested sound volume value defined according to the standard specifications of a Bluetooth.
2. Description of Background Art
A technique for remotely controlling the electronic volume incorporated in an audio terminal by operating a sound volume adjustment key provided on a remote controller is disclosed in Japanese Patent Laid-Open No. Hei 5-308230. A “+(plus)” key and a “−(minus)” key are provided as sound volume adjustment keys on the remote controller. Further, a “MUTE” key for attenuating the sound volume to the lowest level at a single stroke is sometimes provided on the remote controller.
Meanwhile, specifications for remotely controlling the sound volume of a headset for mounting on an individual's head is by means of a remote controller that is set in a Bluetooth which is worldwide communication standards. According to the specifications, 16 steps from “0#” to “15#” are prepared as sound volume adjustment steps (levels).
In sound volume adjustment between a television set and a remote controller therefor, an instruction of an absolute sound volume value is not issued from the remote controller to the television set, but a signal for relatively increasing or decreasing the sound volume at present like “to increase the sound volume level by one step” or “to decrease the sound volume by one step” is outputted. In contrast, a remote controller and an audio terminal which comply with the Bluetooth specifications communicate a sound volume value of one of 16 steps therebetween to recognize the sound volume value pointer therebetween. Then, if the “+” key 49a (as illustrated in FIG. 3) is operated once on the remote controller on which the current value of the sound volume value pointer is “8#”, then “9#” which is higher by one step than the current value of the sound volume pointer is transmitted as a requested sound volume value (Vreq) from the remote controller to the audio terminal.
The audio terminal side changes the sound volume value from “8#” to “9#” and further updates the sound volume value pointer from “8#” to “9#” in response to a reception of the requested sound volume value (Vreq). Further, a notification of a result of the updating of the sound volume value pointer is issued as an actual result sound volume value (Vrep) to the remote controller. The remote controller updates the sound volume pointer from “8#” to “9#” based on the received actual result sound volume value (Vrep). Accordingly, if the “+” key 49a is thereafter operated only once on the remote controller side, then a requested sound volume value (Vreq) “10#” is transmitted from the remote controller to the audio terminal.
When the electronic volume of a headset for a driver of a vehicle is remotely controlled by a vehicle body side remote controller, if it is necessary to operate the electronic volume of the headset by use of a hand (using sound volume keys 39a, 39b, as shown in FIG. 2) with a glove positioned thereon, preferably the number of sound volume adjustment steps is decreased from 16 steps of the standard specifications to make the operation of the electronic volume simple and convenient. For example, it is preferable Japanese Patent Laid-Open No. Hei 5-308230 to decrease the number of sound volume adjustment steps, for example, to such four steps or levels (1# to 4#), as “mute,” “low sound volume level for stopping,” “medium sound volume level for traveling at a low or medium speed” and “high sound volume level for traveling at a high speed.” At this time, in a potentiometer built for controlling electronic volume, predetermined amplification factors (attenuation factors) are allocated to the four sound volume levels (1# to 4#) using sound volume keys 39a, 39b described above.
FIG. 19 is a view illustrating a relationship among the requested sound volume value (Vreq), sound volume value level (L) and amplification factor (Gamp) of the potentiometer of the apparatus disclosed in Japanese Patent Laid-Open No. Hei 5-308230. The amplification factors (Gamp) “19#”, “23#”, “27#” and “30#” of the potentiometer are allocated to the sound volume levels “1#” to “4#”, respectively. In addition, the requested sound volume values (Vreq) “1#”, “5#” “10#” and “15#” are allocated, respectively.
At this time, between the sound volume value levels (L) “1#” and “2#”, the requested sound volume values (Vreq) “1#” to “5#” and the amplification factors (Gamp) “19#” to “23#” are coordinated in a one-by-one coordination relationship. However, between the sound volume value level (L) “2#” and “3#”, while the requested sound volume value (Vreq) includes six steps of “5#” to “10#”, the amplification factor (Gamp) includes five steps of “23#” to “27#”. Accordingly, if “5#” is transmitted as the requested sound volume value (Vreq) from the remote controller, then the audio terminal sets the amplification factor (Gamp) to “23#” and sends back “5#” as the actual result sound volume value (Vrep). Consequently, the remote controller updates the sound volume value pointer to “5#”.
If such a sequence of operations as described above is repeated and “9#” is transmitted as the requested sound volume value (Vreq) from the remote controller, then the audio terminal sets the amplification factor (Gamp) to 27# and sends back 9# as the actual result sound volume value (Vrep). Thus, the remote controller updates the sound volume value pointer to “9#”. Accordingly, if the “+” key 49a is operated further on the remote controller, then “10#” is transmitted as the requested sound volume value (Vreq). However, since “10#” of the requested sound volume value (Vreq) is coordinated with “27#” of the amplification factor (Gamp), although the “+” key 49a has been operated, the sound volume does not vary. Thus, with the conventional apparatus disclosed in Japanese Patent Laid-Open No. Hei 5-308230, the speaker 12 of the audio terminal does not always produce the desired sound volume.